This invention introduces a simple two-step hydrogen fluoride (HF) etching method to enhance the electrical characteristics of liquid-phase deposited fluorinated silicon oxides (LPD-SiOF).
During the development of oxide layer in integrated circuit production, in addition to standard RCA cleaning process, an appropriate surface treatment or etching technique is required to effectively remove native oxide and reduce surface microroughness. When the thickness of oxide layer is reduced to less than 10 nm, silicon (Si) surface should be free of any native oxide and fully hydrogen-passivated to ensure that the oxide layer has a high breakdown field, high charge-to-breakdown, and low leakage current.
We have discovered from the various publications in the literature that common surface cleaning process could be divided into two main groups, i.e., dry etching by R. Kroon (Jpn. J. Appl. Phys. Vol. 36, pp. 5068, 1997) and wet etching by R. K. Chanana and S. K. Srivastava, (IEEE Int. Conf. Plasma Science, pp. 282, 1996). In dry etching, M. Biavati et al. (J. Vac. Sci. and Technol., Vol. B13, pp. 2139, 1995) and G. Y. Pavlov (Mat. Res. Soc. Symp., PV. 386, pp. 321, 1995) have reported that plasma etching not only could effectively remove the oxygen ion (O31) on silicon (Si) surface, it could also increase the value of charge-to-breakdown. However the lattices on the silicon (Si) surface could be damaged by the plasma, resulting in further surface microroughness.
Other latest developments in dry etching include laser cleaning reported by G. Vereecke et al. (4th Int. Symp. Ultra Clean Processing of silicon Surfaces, pp. 187, 1998) or H. Park et al. (Electrochem. and Solid-State Lett., Vol. 1, pp. 77, 1998) reported using various gases including hydrogen fluoride (HF)/methanol (MeOH); ultraviolet (UV)/chlorine gas (Cl2); ultraviolet (UV)/oxygen gas (O2) etc. to clean the Si surfaces. On the other hand, H. Habuka et al. (J. Cryst. Growth, Vol. 186, pp. 104, 1998) suggested cleaning with hydrogen fluoride (HF) or hydrogen chloride gases (HCl (g)) under atmospheric pressure or H2 environment or R. Sugino et al. (J. Electrochem. Soc., Vol. 144, pp. 3984, 1997) mentioned using laser on chloride gas (Cl2) to produce chloride ion (Clxe2x88x92), and the list goes on. These techniques have been proven to remove micro-particles, native oxide, and iron pollutants completely. However when compared to wet etching, this procedure could not solve the problems of total removal of calcium ions and surface microroughness. Therefore some simple and effective wet etching methods still play an important role in integrated circuit (IC) production.
Currently the most effective wet etching method uses the chemically oxidized reaction of hydrogen peroxide (H2O2) on silicon (Si) to form an oxide layer, which will be removed by hydrogen fluoride (HF) etching in the later step. Based on this theory, numerous novel methods have been published in various renowned periodicals: M. Alessandri et al. (4th Int. Symp. Ultra Clean Processing of silicon Surfaces, pp. 27, 1998) suggested hydrogen fluoride (HF)/ultrapure deionized water (D. I. water)/ozone (O3)/ultrasonic cleaning method. T. Hattori et al. (J. Electrochem. Soc., Vol. 145, pp. 3278, 1997) reported using ozone treated D.I. water/diluted hydrogen fluoride (HF). T. Ohmi et al. (IEICE Trans. Electrons, Vol. E75-C, pp. 800, 1992) reported modified RCA cleaning method. T. H. Park et al. (J. Electrochem. Soc., Vol. 142, pp. 571, 1995) reported nitric acid (HNO3)/hydrogen fluoride (HF) cleaning system. S. Verhaverbeke et al. (Symp. VLSI Tech. Dig. Tech. Papers, pp. 22, 1992) suggested the hydrogen fluoride (HF)-last cleaning step. T. Shimono et al. (IEICE Trans Electrons, Vol. E75-C, pp. 812, 1992) mentioned hydrogen fluoride (HF)/hydrogen peroxide (H2O2) method etc. Those cleaning methods could effectively reduce surface microroughness and provide a more completely hydrogen-passivated surface, thus forming an oxide layer of extremely high quality from the furnace oxidation production.
Based on the above articles, the wafer pre-cleaning process in liquid-phase deposition method could be generally divided into two groups: C. J. Huang et al. (J. Vac. Sci. and Technol. Vol. A16, pp. 2646, 1998) reported applying diluted hydrogen fluoride (HF) to remove native oxide, while M. P. Houng et al. (Mater Chem. and Phys., Vol. 59, pp. 36, 1999) suggested immersing in a mixed solution of acetone, methanol, and hydrogen fluoride (HF). Basically these are considered standard RCA cleaning with hydrogen fluoride (HF) etching, and the metal oxide semiconductor (MOS) devices produced generally expressed relatively good electrical characteristics: breakdown field of 8xcx9c9 MV/cm and interface electrical chargexcx9c1011 eVxe2x88x921cmxe2x88x922. However there are yet to have articles related to the effects of surface treatment or etching on the characteristics of liquid-phase-deposited silicon oxides (LPD-SiOF). As the growth mechanism of liquid-phase deposition differs from furnace oxidation method, the surface quality will directly affect the deposition of silicon oxide film that will then enormously affect the interface characteristics.
The proposal of our invention will not only maintain the high quality in silicon oxide (SiO2) film and extend the application ranges of liquid-phase deposition method, it could provide further development in future ultra-large-scale integrated circuit (ULSI) production especially in gate oxide layer.
Our proposal introduces a kind of simple two-step hydrogen fluoride (HF) etching method that could improve the electrical characteristics of liquid-phase-deposited fluorinated silicon oxides (LPDxe2x80x94SiOF) including effective removal of native oxides, lowering of interface trap density (xcx9c1010 eVxe2x88x921cmxe2x88x922), reduction of surface microroughness (Ra=0.1 nm), and raising of breakdown field (xcx9c9.7 MV/cm).
While the invention is susceptible to various modifications and alternative forms, certain illustrative embodiments thereof have been shown by way of example in the drawing and will herein be described in detail.